Why was the Super-Insulated Shell Selected?
Exterior or Interior Insulation? First the team analyzed whether interior or exterior insulation was more appropriate for Castle Square. They discovered that an external super insulated shell creates significantly higher energy savings than insulation applied to the inside walls of the apartments. This is because when insulation is applied to the outside of a building, it can cover the entire surface are of a building. With external insulation, the entire building gets insulated. There are no gaps.
In contrast, when insulation is applied to the inside wall of an apartment, it only covers the area of the wall. The insulation cannot be installed inside the floor/ceiling cavity, so there are still large gaps in the building where this is no insulation. There is a also a lot of thermal bridging. At Castle Square, apartments have concrete floors. These concrete floors connect directly to the outside surface of the building. With external insulation, this direct contact with the outside of the building (i.e., thermal bridge) stops because this surface is insulated. In contrast, if only the interior apartment walls are insulated, heat loss will continue from the floors to the outside of the building.
External insulation was a no brainer in terms of energy savings. Additionally, interior insulation proved impractical at Castle Square because it is an occupied rehab (i.e., a renovation where residents and all their furniture and possessions stay in the apartment during construction). The team made this determination after actually installing wall insulation in an apartment. Dust alone from new drywall would have posed a potentially negative health consequence for residents. Plus moving and protecting furniture to access the wall surface with insulation would have been difficult.
Selecting the Exterior Insulation System – Once it was determined that an external insulated shell would be used, the team explored three shell insulation options – 1) prefabricated metal panelized system (This is what we selected.); 2) EFS; and 3) fabrication of metal panels on site.
During the beginning of design, the team considered the EFS methodology, because at first it appeared to be the least expensive system. The team decided not to use the product, partially because of concern for ongoing maintenance requirements. However, the biggest issue was that our insurance carrier determined that EIFS would change the fire rating of the building. A brick building (the pre-renovated Castle Square) is less expensive to insure, because brick is not very susceptible to fire. However, EIFS (like wood and other materials) is more susceptible to fire than brick, so insurance carriers charge more to insure a building with this siding. Amazingly enough, the increase in annual insurance premium was so high that the additional cost of insurance would have eaten up most of the money we would have saved on heating and cooling costs!!!
An on-site fabricated panel was also eliminated, because of warranty issues associated with building something unique in the field.
In the end, the team chose the prefabricated insulated metal panel because it is extremely long lasting and durable, requiring almost no maintenance; it meets all performance requirements; and it retains the building’s original fire rating, adding zero additional insurance costs to the property.